Field of the Invention
The present invention relates to a fluoride fluorescent material and a method for producing the same as well as a light emitting device using the same.
Description of the Related Art
A light emitting diode (LED) is a semiconductor light emitting element frequently used as a substitute for a conventional light source, and is useful as a display lamp, a warning lamp, and a lamp for indicator or lighting. Various types of light emitting devices emitting light of, e.g., white color, electric bulb color, or orange color have been developed, wherein the devices use a semiconductor light emitting element produced from a Group III-V semiconductor, such as gallium nitride (GaN), and a fluorescent material in combination. These light emitting devices emitting light of white color or the like is controlled in color tone by the principle of mixing colors of lights. As a system for emitting a white light, a system using a light emitting element emitting an ultraviolet light and three types of fluorescent materials respectively emitting red (R), green (G), and blue (B) lights, and a system using a light emitting element emitting a blue light and a fluorescent material emitting, e.g., a yellow light have been well known. A light emitting device of a system using a light emitting element emitting a blue light and a fluorescent material emitting, e.g., a yellow light is demanded in a wide variety of fields, such as a lighting, a car lighting, a display, and a backlight for liquid crystal. In these fields, the fluorescent material used in the display application is desired to have both excellent light emission efficiency and excellent intensity of color for reproducing colors in a wide range on the chromaticity coordinates. Further, the fluorescent material used in the display application is desired to be advantageously used in combination with a filter, and thus a fluorescent material exhibiting an emission spectrum having a narrow half band width is demanded.
For example, as a red light-emitting fluorescent material having an excitation band in the blue region, and exhibiting an emission spectrum having a narrow half band width, a fluoride fluorescent material activated by tetravalent manganese ions (Mn4+), having a composition, such as K2TiF6:Mn4+, Ba2TiF6:Mn4+, Na2TiF6:Mn4+, or K3ZrF7:Mn4+, has been known (see, for example, Japanese Patent Application prior-to-examination Publication (kohyo) No. 2009-528429). In addition, a fluoride fluorescent material having a composition: K2SiF6:Mn4+ has been known (see, for example, Japanese Unexamined Patent Publication No. 2010-209311). Further, the excitation and emission spectra and the light emission mechanism of a fluoride complex fluorescent material activated by Mn4+ have been known (see, for example, “Effective Mn(IV) Emission in Fluoride Coordination”, written by A. G. Paulusz, J. Electrochemical Soc., 120 N7, 1973, p. 942-947).